The present invention relates to the field of titration for determining the concentration of an unknown material in a solution by stoichiometric reaction of a known titrant with the unknown titrate and recognition of the endpoint. In a particular aspect, the invention is directed to an automatic titration system and method for use in on-stream process monitoring and control applications. Not only is the system and method for the invention capable of performing routine and repetitive titrations at a faster rate than is presently achieved by semiautomatic or manual methods, but with microprocessor control, according to another aspect of this invention, greater flexibility and reliability with more complex titrations maybe obtained.
In the basic laboratory titration procedure, the titrant is accurately volumetrically added, such as by a buret, to a predetermined volume or weighted portion of the sample unknown to react therewith until the endpoint is reached and observed, usually visually as by an indicator color change. Some attempts at applying automatic titrators in industrial process applications are discussed in "Automatic Titrators", J. P. Phillips, Academic Press, New York, 1959. Many of these attempts have merely involved laboratory techniques through the use of complex mechanical components that record a titration curve, or stop the titration at the endpoint by mechanical or electrical means, instead of by manual attention. These devices and methods are more properly considered semiautomatic where sample preparation, addition of sample to the device, removal of sample, and cleaning of the titration chamber between titrations must be performed manually. Even a continuous titrator utilizing feedback principles through application of a servomechanism requires accurate metering of a portion of the process stream into the reaction or titration chamber together with controlled metering of a titrant reagent in such a manner as to maintain a balanced condition. The large volumes of standard reagent required in these processes necessitate skilled and time consuming manual attention.
The need for preparation of standard solution and the utilization of complex hardware such as volumetric metering pumps and motor driven burets employed in automated volumetric titration techniques may be overcome through the use of coulometric titrant addition wherein the titrant reagent is continuously generated. In such a procedure, the more easily measured and controlled electric current used over a period of time relates to the quantity of, and in essence functions as, the titrant. Nevertheless, since volumetric sampling is still required in such a procedure, automating this technique in the past has involved complex mechanical components involving critical liquid delivery systems and delicate mechanical hardware having small liquid ports, all of which requires high maintenance.
The automatic titration system and method according to the present invention overcomes many of the difficulties encountered with the previous devices and methods for automatic titration and results in advantages not heretofore obtained. The present invention provides an acceptable industrial automatic process titrator capable of continuous unattended operation at the process site and which is easily serviceable due to the elimination of complex precision mechanical components. The automatic titration system of this invention receives samples, performs analyses, and communicates with monitoring or control equipment quickly and reliably so that titrations can be repeated at a high rate of one cycle in approximately 2 minutes. In addition, the automatic titration system and method of this invention advantageously lends itself to microprocessor control over the titration reaction and titrator sequencing in accordance with another specific aspect of the invention.